I want to share my VPN connection with other devices. I just got a D-Link router, and I'm a little bit lost about how to deal with it. I connect to internet using the VPN of my university (PPTP). The LAN has a DHCP server, giving to each computer an IP address according to their MAC address (if the mac address is unknown by the DHCP server, then it gives an IP address under a subnetwork that cannot connect to the VPN). The connection to internet can be successful only if the combination IP:VPN_login:VPN_password is correct.

I already connected to the router, using telnet on port 23. I know how to change MAC address using ifconfig ethx down && ifconfig ethx up hw ether <mac address>. So changing the mac address of the router to mine (which is recognized by the university), the router will get my usual IP address.
But now?
To connect to vpn, I usually use network-manager on ubuntu, and the toolkit nmcli